Lan Fleming wrote:
Why would that be interesting? These people are amateure researchers working in their spare time. It's not interesting, that they didn't have a vast collection of references; it's irrelevant.

Alex writes:
It may irrelevant to you, but not to me. Even if the authors are "amateure [sic] researchers", they are responsible for the references, as are you as "editor." At any rate, if, as you suggest, the work is amateur and the researchers do not have access to "a vast collection of references" then why should any professional scientist pay attention to it?

Lan Fleming wrote:
What are the frame numbers that show this? I haven't seen such streaks passing through any craters wider than the streaks themselves in the images I've looked at.

Alex writes:
Non sequitur. Your comment above makes no sense. I simply stated that "...MOC NA imagery of the dark streaks...show no pooling where the streaks descend across craters or other topographical lows." You failed to address this.

Lan Fleming wrote:
It's not at all problematic for a liquid to spread out from the point of origin in all directions until the surface tension and the pressure of the liquid layer balance as the layer thins out. Try releasing a small stream of water from an eye dropper on the side of a sink basin.

Alex writes:
Irrelevant. Try doing this at the ambient pressures, temperatures, and gravity of Mars. The inside of your putative "sink basin", presumably on Earth, though you do not specify this, has no bearing on the behavior of a released liquid in the Martian environment.

Lan Fleming wrote:
The explosiveness of the release would be in part related to the thickness of whatever is blocking the flow. I don't see any reason off-hand why all water releases would have to be violent.

Alex writes:
Are you serious? I'll give you an "off-hand reason": The ambient pressure at the Martian surface in the vicinity of these dark streaks, many of them at relatively high altitudes on Mars, require that any liquid water stored in the near surface be capped by lithostatic overburden sufficient to overcome any diffusivity contact with the atmosphere. Further, the depth to the melting isotherm (at least many hundreds of meters, if not more) argue that the hydraulic pressures must be substantial. Try uncapping this to the millibar atmospheric pressures and see whether "all water releases would be... violent." If not, then why wouldn't the water simply vaporize before "seeping"?

Lan Fleming wrote:
To the contrary, the lack of evidence for any relief is one of the characteristics that indicate a slow "seepage" of liquid that does not carry away large quantities of debris like a raging flood would do. A slow seepage could flow a very long way, given a surface that is not very absorbent and a liquid that isn't very viscous.

Alex writes:
True, to first order the lack of margin relief is supportive of the "wet" origin. However, when compared to the run out distances this lack of relief is not compatible with the behavior of a non-catastrophic flow of liquid water across the Martian surface.

Lan Fleming wrote:
The lack of relief is far more a problem for the dust slide interpretation...

Alex writes:
Not really. During a dust slide (or even a terrestrial avalanche), if the rate of mass lost to the atmosphere is balanced by mass continually entrained as the avalanche front desends, then it is no surpise that there is no relief. In fact, I've personally seen snow avalances that leave virtually no trace after passage. Moreover, if, as soon-to-be-published work suggests, the dark streaks on Mars "involves renewable sources of dust only", then it is not at all inconsistent to see the underlying substrate(s) or superjacent surfaces unaffected by the slides.

Lan Fleming wrote:
Malin's interpretation of the gullies as water related was criticized because there were no indications of water flow elsewhere. Maybe there are such indications of water in these streaks at equatorial latitudes. The mechanism might be different at different latitudes.

Alex writes:
Perhaps, but this requires more data on the Martian subsurface, which we do not have. In any event, I noted the streaks do not seem to correlate to any specific type of geologic unit. If so, then why should the mechanism for water release be latitude dependent during the same geologic epoch and/or obliquity cycle?

Alex R. Blackwell
University of Hawaii